> A typical example is that Uber had a team to implement their own Bazel-like system because "Bazel (or any other tool) does not scale in Uber-scale"

Citation needed? AFAIK Uber was using Facebook's Buck and decided to move to Bazel for stacks where Buck is admittedly not good at (e.g. Go). I'm not aware of any org within Uber reinventing Bazel. The web org might be closest to what you're claiming, but even there, it merely wraps over Bazel to bridge over its shortcomings (i.e. package management is typically done "outside" of Bazel, via yarn/npm in web, as seen in the official rules_nodejs and other 3rd party spin-off rulesets)